Speed reducer with electric motor

Abstract

In a speed reducing unit with an electric motor, a speed reduction mechanism has: an elliptical cam that rotates together with a rotating part; a flexible external gear that deforms according to the rotation of the elliptical cam; a flexible bearing that is located between the elliptical cam and the flexible external gear; and a movable internal gear that rotates together with an output part. The flexible external gear and the movable internal gear are engaged with each other. The electric motor has: a rotor holder that is part of the rotating part and that rotates together with the elliptical cam; a rotor magnet that is fixed to the rotor holder; and a stator that is fixed to a casing. The rotor holder has a rotor-holder lid part, and the positions of the rotor-holder lid part and the flexible bearing in the axial direction at least partially overlap.

The invention claimed is: 
     
       1. A speed reducing unit with an electric motor, comprising:
 a casing; 
 an electric motor having a rotating part that rotates around an axis of the casing; 
 a speed reduction mechanism that transmits a rotational motion of the electric motor while decelerating the rotational motion; 
 an output part that rotates at a decelerated rotation speed; 
 a first bearing that rotatably connects the casing or a member fixed to the casing to the rotating part; and 
 a second bearing that rotatably connects the casing to the output part, 
 wherein the speed reduction mechanism is a speed reduction mechanism having: 
 an elliptical cam that rotates together with the rotating part, 
 a flexible external gear that deforms according to the rotation of the elliptical cam, 
 a flexible bearing that is located between the elliptical cam and the flexible external gear, and 
 a movable internal gear that rotates together with the output part, 
 in which the flexible external gear and the movable internal gear are engaged with each other, and the flexible external gear and the movable internal gear rotate relative to each other due to a difference in the number of teeth, and 
 wherein the electric motor has: 
 a rotor holder that is part of the rotating part and that rotates together with the elliptical cam, 
 a rotor magnet that is fixed to the rotor holder, and 
 a stator that is fixed to the casing or a member fixed to the casing and that is opposed to the rotor magnet, 
 in which the rotor holder has a rotor-holder lid part that is opposed to the stator in an axial direction directly or via another member, and 
 positions of the rotor-holder lid part and the flexible bearing in the axial direction at least partially overlap. 
 
     
     
       2. The speed reducing unit with an electric motor according to  claim 1 ,
 wherein the elliptical cam and the rotor holder are connected together. 
 
     
     
       3. The speed reducing unit with an electric motor according to  claim 1 ,
 wherein the elliptical cam and the rotor holder are connected together, and 
 wherein the rotor holder has: 
 a cylindrical fixing part that is positioned at an inner end of the rotor-holder lid part and is fixed to a shaft, and 
 a tubular part that is positioned at an outer end of the rotor-holder lid part and hanging downward from the rotor-holder lid part in the axial direction, 
 wherein the tubular part has the elliptical cam. 
 
     
     
       4. The speed reducing unit with an electric motor according to  claim 3 , comprising:
 an enlarged diameter part having a diameter increasing toward an upper side in the axial direction at a portion of the fixing part connecting to the rotor-holder lid part. 
 
     
     
       5. The speed reducing unit with an electric motor according to  claim 3 ,
 wherein the rotor-holder lid part has a connecting part whose thickness in the axial direction increases toward the tubular part. 
 
     
     
       6. The speed reducing unit with an electric motor according to  claim 3 ,
 wherein the tubular part has a groove positioned below the elliptical cam and an annular part positioned below the groove. 
 
     
     
       7. The speed reducing unit with an electric motor according to  claim 1 ,
 wherein there is a groove between the elliptical cam and the flexible bearing. 
 
     
     
       8. The speed reducing unit with an electric motor according to  claim 1 ,
 wherein the rotating part has a shaft disposed coaxially with a center axis, and 
 wherein the rotor holder and the shaft are connected together.